In the related art, there has been known an image reading device including a housing mounted at an upper surface thereof with a document table glass and an image reading unit configured to be received in the housing to be movable in a sub-scanning direction perpendicular to a main scanning direction. The aforementioned image reading unit has a light source, which emits light toward the document table glass, and the like. The image reading unit is connected to a fixed board, which is fixed to a bottom wall of the housing, via a flat cable. One end part of the flat cable is connected to the image reading unit and the other end part thereof is connected to the aforementioned fixed board. The flat cable includes a flexible member and forms an U shape having an upper sidewall part, a lower sidewall part, and a curved part that connects the both sidewall parts to each other when viewed from the main scanning direction. With the movement of the image reading unit, the flat cable is deformed while increasing/decreasing a curvature radius of the curved part.
In this type of image reading unit, when the curvature radius of the curved part of the flat cable becomes equal to or more than a predetermined value during the movement of the image reading unit, an upper surface of the upper wall part of the flat cable contacts with the document table glass. As a consequence, frictional resistance or electrostatic attraction force occurs between the flat cable and the document table glass. When the electrostatic attraction force occurs, the cable may operate to repeat a close contact state and a separation state with respect to the glass surface. Due to the frictional resistance or the electrostatic attraction force, there is a problem that a movement speed of the image reading unit is changed.
In order to solve such a problem, various technologies have been proposed up to now. For example, in an image reading unit disclosed in Patent Literature 1, a weight is mounted at a lower surface of the upper wall part of the flat cable. In this way, the upper wall part of the flat cable is bent downward by the load of the weight, so that a contact between the flat cable and the document table glass is avoided.